1. Field of the Invention
The present invention relates to a stereoscopic image display technique. More specifically, the present invention relates to a stereoscopic image display device, a stereoscopic image display method, and a stereoscopic image display program for displaying stereoscopic images without giving a sense of discomfort to the observer even when the relative distance between the stereoscopic image display device placed on a back face part of a seat and the observer changes.
2. Description of the Related Art
Recently, small and middle sized displays are placed on each of the back face parts of passengers' seats of airplanes and long-distance trains, so that each passenger can view favorite program contents by using the display provided on the back face part of the respective front seat.
There are many stereoscopic image display contents contained in the program contents for the passengers, typically movie films. Thus, it is desired to be able to display stereoscopic images on the displays placed on the back face part of the seats.
Note here that there are an eyeglass type and a naked-eye type as the stereoscopic image display devices having a display for displaying stereoscopic images.
With the eyeglass type stereoscopic image display device, the observer wears eyeglasses for stereoscopic image display and images of different parallaxes are projected to the left and right eyes to display stereoscopic images for the observer. However, there are many observers who feel a sense of discomfort to wear the eyeglasses for stereoscopic image display, and the naked-eye type stereoscopic image display device which does not requires such eyeglasses is more desired.
With the naked-eye type stereoscopic image display device, it is typical to use a method which projects images of different parallaxes to the left and right eyes of the observer through dividing a spatial region for projecting a stereoscopic image and projecting images of different parallaxes to each of the divided spatial regions.
With such method, employed is a technique which provides a lenticular lens, a parallax barrier, or the like as an optical light-ray separating module to the stereoscopic display panel of the stereoscopic image display device to separate the image to be projected for each spatial region so as to project images of different parallaxes to each of a plurality of the spatial regions.
The stereoscopic image display device provided with the optical light-ray separating module such as a lenticular lens or a parallax barrier does not require the eyeglasses for stereoscopic image display, so that it is excellent in respect that the user feels no sense of having a trouble.
However, the spatial region where the observer can visually recognize a stereoscopic image properly (a normal stereopsis viewable region) is limited to a case where the position of the left eye of the observer is within a spatial region to which a left-eye image is projected and the position of the right eye of the observer is within a spatial region to which a right-eye image is projected.
When the position of the left and right eyes of the observer is shifted out from the normal stereopsis viewable region, the left-eye image and the right-eye image may be viewed in an overlapped manner (a double image (CT-image) caused by the so-called 3D crosstalk) and a stereoscopic image of reversed sense of depth may be viewed (the so-called pseudoscopic view).
Other than those, another issue known to be generated with the naked-eye type stereoscopic image display device is that luminance unevenness (luminance fluctuation) occurs on the surface of the stereoscopic display panel when the observing position of the observer is shifted out from the normal stereopsis viewable region and an image region that is displayed still darker than the peripheral image region appears within the stereoscopic image.
This phenomenon is called 3D moiré, which is caused when a non-display region (a light-shielding part generally called a black matrix in a liquid crystal panel) between pixels for each of the viewpoints is visually recognized by being interfered with the optical light-separating module such as the lenticular lens or the parallax barrier. That is, 3D moiré is periodical luminance unevenness (may sometimes indicate color unevenness) caused by projecting different images to different angular directions.
3D moiré is the fluctuation in the angular direction of the luminance (luminance angular fluctuation), which may not be an issue depending on the observing positions. However, when the luminance angular fluctuation in the angular direction is large, the display quality of the stereoscopic image is deteriorated so that the observer feels a sense of discomfort.
The issues of CT-images and pseudoscopic view caused by 3D crosstalk and the issues of 3D moiré (referred to as “each issue in 3D display” hereinafter) which are peculiar to the naked-eye type stereoscopic image display device depend on the relative distance between the stereoscopic image display device and the observer.
Further, there may be cases where the backrest in the back face part of the passenger's seat may be inclined due to the convenience of the passenger of the front seat in an airplane, a train, or the like. Accordingly, the stereoscopic image display device placed on the back face part is moved.
Thus, in a case where the stereoscopic image display device is placed on the back face part of a seat, the relative distance (observing distance) between the stereoscopic image display device and the observer is changed rapidly due to the convenience of the passenger of the front seat even when the observer does not move. Thereby, each of the issues of the 3D display occurs, so that the display quality of the stereoscopic images is deteriorated greatly. This deterioration in the display quality gives a sense of discomfort to the observer, so that there is a strong demand for a stereoscopic image display device with which each of the issues of the 3D display does not occur even when the observing distance changes.
As a technique for lightening the influences of each of the issues of the 3D display, there is considered a structural content in which: the observing distance showing the relative distance between the stereoscopic image display device and the observer and the observing position showing the relative position of the observer with respect to the stereoscopic image display device are calculated by measuring the position of the observer; and the display setting of the stereoscopic image is adjusted according the information regarding the calculated observing distance or observing position. When such structure is employed, a device for measuring the position of the observer is required since the observing distance information or the observing position information is used.
Especially, in order to lighten the influences of the CT-images as well as pseudoscopic views caused by the crosstalk and the influences of the 3D moiré more effectively, it is necessary to measure the observing distance showing the depth-direction distance between the observer and the stereoscopic image display device. As the device for measuring the observing distance, there is known a measuring device (a three-dimensional position measuring device) which is capable of measuring the position on the three-dimensional space by measuring the depth-direction distance.
Recently, the prices of such three-dimensional position measuring devices have been lowered. However, compared to USB cameras (small camera modules of mobile apparatuses) capable of capturing the position of the observer as captured image data on a two-dimensional plane, tilt sensors for measuring the inclined state of a seat, etc., the measuring devices are still expensive.
That is, to provide such expensive measuring device to the stereoscopic image display device leads to an increase in the entire device cost, which is a cause for hindering popularization of the stereoscopic image display devices placed on the back face parts of the seats.
As the techniques related to overcoming such issues, following contents (Patent Documents 1 to 9) are known, for example.
Japanese Unexamined Patent Publication 2009-75842 (Patent Document 1) discloses a technique which calculates the observing position including the observing distance from the state of the seat of the observer and the captured images acquired by an in-vehicle camera attached to a back mirror for correcting distortions generated by image tailing generated when the display surface is observed from oblique directions.
WO 2012-023509 (Patent Document 2) discloses a technique which, in a calibration system for adjusting the position and posture of a display according to the position of the observer, calculates the relative position of the observer with respect to the display by measuring an infrared ray emitted from the display by an infrared camera placed at the position of the observer.
Japanese Unexamined Patent Publication 2000-152285 (Patent Document 3) discloses an image processing technique which measures the position of the observer from captured image data picked up by a camera for displaying stereoscopic images without giving a sense of discomfort even when the observer moves. Further, as a processing method of this technique, there is also depicted a method of adjusting the focal distance of the camera for capturing a face image within an arbitrary image range other than the image processing method which measures the position of the observer from the captured image data on a two-dimensional plane.
Japanese Unexamined Patent Publication 2012-170502 (Patent Document 4) discloses a technique which informs the observer to move to a spatial region where stereoscopic images can be visually recognized when the position of the observer is shifted out from the spatial region where the stereoscopic images can be visually recognized properly.
At the stereoscopic image display device according to Japanese Unexamined Patent Publication 2008-15188 (Patent Document 5), a tilt sensor such as an acceleration sensor is placed in order to provide the stereoscopic images without giving a sense of discomfort even when the observer moves. That is, disclosed is a technical content in which the tilt of the stereoscopic image display device is detected by the tilt sensor and the observing position is measured.
Japanese Unexamined Patent Publication 2008-279155 (Patent Document 6) discloses a technique which adjusts the placed angle of the display surface by considering the tilt angle between the seat of the observer and the front seat in order to align the display direction of the display surface and the direction of the sight of the observer even when the display direction of the display surface placed at the back face part of the front seat changes due to the change in the reclining state of the passenger at the front seat.
The stereoscopic image display devices according to Japanese Unexamined Patent Publication 2014-45474 (Patent Document 7), Japanese Unexamined Patent Publication 2014-45473 (Patent Document 8), and Japanese Unexamined Patent Publication 2014-44396 (Patent Document 9) employ a technique which lightens the influences of CT-image as well as pseudoscopic views caused by the crosstalk and the influences of the 3D moiré to display stereoscopic images without giving a sense of discomfort through performing image conversion processing on the right-eye image and the left-eye image in accordance with the position of the observer even when the position of the observer is shifted.
Further, S-H. Ju, et al, “Viewer's Eye Position Estimation Using Camera” 2013 International Symposium Digest of Technical Papers, 48.3, pp 671-674 (Non-Patent Document 1) discloses a technique which, for measuring the observing position only with an inexpensive measuring device, registers in advance the actual distance between the pupils of the observer, and compares the distance between the pupils of the observer shown in the captured image data on a two-dimensional plane captured by a USB camera or the like with the distance between the pupils of the observer registered in advance to calculate the observing distance that shows the distance in the depth direction between the stereoscopic image display device and the observer.
However, the observing position calculating method depicted in Patent Document 1 is a technique used on the assumption that the set positions of the in-vehicle camera and the display are fixed, so that it cannot be employed in a case where the set position of the display moves depending on the convenience of the passenger at the front seat (e.g., in a case where the display placed at the back face part of the seat is used).
Further, with the technique disclosed in Patent Document 2, it is necessary to place an infrared camera at the position of the observer. Thus, it is difficult to place the measuring device, and the device cost is increased.
Incidentally, in order to lighten the influences of the CT-images as well as pseudoscopic views caused by the crosstalk and the influences of the 3D moiré more effectively, it is necessary to measure the observing distance showing the depth-direction distance between the observer and the stereoscopic image display device. However, in Patent Document 3, there is no method disclosed for measuring the distance in the depth direction between the stereoscopic image display device and the observer from the captured face image. Therefore, it is not possible to display fine stereoscopic images without giving a sense of discomfort even if the technique disclosed in Patent Document 3 is employed.
With the technique disclosed in Patent Document 4, a distance sensor is used for measuring the observing distance. Thus, the cost for the measuring device is increased.
Further, while the technique for detecting the tilt angle of the stereoscopic image display device by using the tilt sensor is depicted in Patent Document 5, there is no method disclosed for measuring the observing distance by using the inclining angles of the seat of the observer and the seat in front thereof. Therefore, even with the use of the technique disclosed in Patent Document 5, it is not possible to measure the relative distance between the stereoscopic image display device placed at the back face part of the seat and the observer only with an inexpensive measuring device.
The technique disclosed in Patent Document 6 employs the method which calculates the relative angle between the display direction of the display surface and the direction of the eyesight of the observer from the inclined angle between the seat of the observer and the front seat. However, there is no content disclosed regarding calculation of the distance in the depth direction between the display surface and the observer.
Unlike the case of a normal image display device (a display which displays two-dimensional images), the display quality is greatly deteriorated in a naked-eye type stereoscopic image display device due to the influences of CT-images as well as pseudoscopic views caused by the crosstalk and the influences of the 3D moiré not only in the case where the relative angle changes but also in the case where the observing distance changes. Thus, even with the use of the method disclosed in Patent Document 6, it is not possible to lighten the influences of CT-images and pseudoscopic views caused by the 3D crosstalk and the influences of the 3D moiré, which are peculiar to the naked-eye type stereoscopic image display device.
The techniques disclosed in Patent Documents 7 to 9 do not employ the structure in which the inclined angle between the seat of the observer and the front seat is used when measuring the observing position showing the relative distance between the stereoscopic image display device and the observer. Thus, even if such techniques are employed in a state where the stereoscopic image display device is placed at the back face part of the seat, the observing distance cannot be measured only by the use of an inexpensive measuring device.
Further, while it is possible with the technique depicted in Non-Patent Document 1 to measure the observing distance only by the use of an inexpensive measuring device, it is necessary to register in advance the distance between the pupils of the observer to the stereoscopic image display device prior to the measurement. Therefore, in a case where the technique is employed for highly public stereoscopic image display devices used by a great number of observers, it is necessary to register the distance between the pupils every time the observer changes, which makes the processing complicated. That is, when the technique in which no method for easily registering the distance between the pupils of a great number of observers is not disclosed at all is applied to highly public stereoscopic image display devices and the like, the advantages thereof cannot be brought out.
It is therefore an exemplary object of the present invention to overcome the above-described issues and, more specifically, to effectively lighten the influences of CT-image as well as pseudoscopic views caused by the crosstalk and the influences of the 3D moiré by an inexpensive structure so as to provide a stereoscopic image display device which displays significant stereoscopic images without giving a sense of discomfort to observers, a display method thereof, and a display program thereof.